Apparatus and method for welding and inspecting coiled tubing

ABSTRACT

An apparatus and method for use in welding together sections of coiled tubing ( 6 ) in the oil industry, wherein the apparatus has a container ( 14 ), legs ( 12 ) which can be adjusted to adjust the height of the container ( 14 ), welding apparatus in the container and slots in the walls of the container. In use the container is raised to the height of the coiled tubing which is to be joined. A winch pulls the ends of the coiled tubing towards a clamp, which holds the two ends of the coiled tubing fixed inside the container, while the ends are welded together. The slots in the walls allow the joined tubing to pass out of the container after the weld is completed. The container provides a controlled environment for welding and weld inspection.

Coiled tubing is used in the oil well industry. Coiled tubing (C.T.) ishandled using C.T. units.

The C.T. unit (illustrated in FIG. 1) is a hydraulically-poweredtransportable system including the following main components:

Tubing injector head 1 and tubing guide 91

Tubing reel 2 with counter 92

Blow-out preventer stack 3

Hydraulic power skid 4

Control console 5 connected to power pack 90

Such C.T. units are known in the prior art.

The coiled tubing 6 itself is a continuous tube presently available indiameters from 25 mm (1″) up to 168 mm (6 ⅝″) and available in materialsranging from the most common material which is A606 Type 4, modifiedHigh Strength Low Alloy Steel to Titanium, which is less commonly usedto date.

This continuous length of steel tubing is wrapped onto reels ranging indiameter from 2.3 m (90″) to 5.2 m (204″) or more.

During operation the tubing is fed over the tubing guide 1, through thehydraulic drive tubing injector 4, down through the blow out preventer 3and into the well head.

The flexibility of C.T. operations in terms of application, cost, rigset up time an the ability to remove a tubing string from one well andreuse it in another gives C.T. an unrivalled attraction to platformoperators. C.T. is now being used more frequently to drill new wells,both vertical wells and wells which require the C.T. at certain depthsto deviate towards the horizontal, otherwise known as directionaldrilling or deviated wells, at depths of up to 8000 m (25,000 feet) butcan also be used in many other applications, such as:

Nitrogen Lifts

Acidising

Well Cleanouts

Cementing

Fishing

Logging

Drilling

Velocity Strings

Production Strings

Pre-perforated Liners

Gas Lifts

Gravel Packing etc

New applications for C.T. are being explored constantly as new down holetools are designed and new and better

C.T. materials are developed.

C.T. only really began to take off in the 1980s as great improvementswere made to the reliability of the technology.

The real catalyst came in the mid 1980s when the oil price crashed to$10 per barrel. C.T. was shown to cut costs by 50-85% over conventionalrig operation using a drilling derrick.

During normal operating the C.T. sometimes has to be cut to remove adamaged length of pipe. In the case of very deep wells one length oftubing, say 3000 m (10,000 feet), may have to be joined to anotherlength of 3000 m (10,000 feet) to make a 6000 m (20,000 feet) string ofC.T.

The job of cutting and re-welding the C.T. together in a hostileenvironment is not straightforward and can present practical problems.

At present the normal practice is to refrain from cutting the C.T.unless absolutely necessary and, if welding is required, the welder doesthe best he can, making sure high quality control standards are used.The reason for this is that C.T. butt welds must be completely defectfree. Onshore in a dry, well lit, draught free fabrication shop, withthe welder having to be elevated to get at the C.T. it is a complexoperation.

However in on-site conditions, such as in the desert at +40° C. withhigh winds or on an offshore platform at −20° C. in heavy weather it isvery much more difficult. It can take as much as 10 days to complete aC.T. welding operation in a hostile environment.

At present the main reason for trying to avoid cutting and re-weldingcoiled tubing is because the C.T. has a residual bend in it when takenoff the reel, i.e. if a piece a metre long is cut and placed on thefloor, it forms an arc. If the same is done with another piece and thetwo pieces are welded together, a dog-leg in the C.T. string can becreated, as illustrated in FIG. 2.

This dog-leg 7 created during the welding operation creates a weak pointin the continuous C.T. string which can and does result in the tubingfailing at this point. The perfect weld can only be achieved by weldinga substantially straight length of tubing to another substantiallystraight length of tubing, with the operation being carried out in awell lit, dry stable environment, free of draughts, with goodventilation and an ambient temperature of around 20° C.

There exists a requirement for an apparatus which will provide suchconditions in any environment in which coiled tubing operations arecarried, such that coiled tubing can be welded in a fraction of the timecurrently taken, at a reduced direct cost and at the highest standardpossible.

There exists a requirement that such apparatus will be completelytransportable and self contained, such that it can be transported to thesite of the C.T. operations, kept there for the duration of theoperations, and then removed to another site.

It is an object of the present invention to provide an apparatus andmethod which will provide controlled conditions for the welding andinspection of coiled tubing joints in any environment in which coiledtubing operations are carried out.

According to a first aspect of the present invention there is provided aportable unit for on-site welding operations comprising a container forcarrying out welding operations therein, a tube clamping means andwelding apparatus, said container having a roof, two opposing side wallsand at least one door therein.

Preferably the container comprises a slot in each of said opposingwalls, each of said slots being adapted to allow the passage of a tubeextending through said wall and clamped by said clamping means, suchthat said tube may move relative to said container. Said slots may besubstantially horizontal and extend to an opening in an end wall of saidcontainer. Alternatively said slots may be substantially vertical andextend to a further slot provided in said roof.

Preferably the unit comprises means for adjusting the height of saidcontainer, most preferably height adjustable legs.

Preferably the tube clamping means is adapted to clamp two sections oftubing in abutting end to end relationship. Preferably the tube clampingmeans comprises a moveable clamp assembly adapted to hold and move afirst one of said sections of tubing axially into abutting end to endrelationship with a second one of said sections of tubing. Preferablythe tube clamping means further comprises a fixed clamp assembly adaptedto hold the second section of tubing.

The unit may comprise a first guide means adapted to guide the tubeclamping means between a first position outside the container and asecond position inside the container.

The unit may further comprise a tube straightening means. The unit mayfurther comprise a second guide means adapted to guide the tubestraightening means between a first position outside the container and asecond position inside the container. Preferably the first guide meansis operable independently from the second guide means.

Preferably the container comprises a door which is retractable over saidopening. The door may be a sliding door, a roller shutter door or otherdoor, and may be adapted to seal the container when the tube clampingmeans is in said second position inside the container.

The tube straightening means may comprise two drive belts arranged suchthat a first driving surface of the first belt is opposed and parallelto a second driving surface of the second belt and is spaced therefrom,the first driving surface having a convex shape in the drive directionand the second driving surface having a concave shape in the drivedirection.

Preferably both the first and second driving surfaces have a concaveshape perpendicular to the drive direction.

Preferably each drive belt is arranged on a jaw member, the jaw membersbeing operable between an open position, in which a tube member may beinserted between the first and second driving surfaces, and a closedposition, in which the first and second driving surfaces clamp a tubularmember positioned therebetween.

Preferably the tube straightening means is pivotally connected to thesecond guide means and can pivot between an operating position in whichthe drive direction is aligned with the clamping means and anon-operative position in which the drive direction is not aligned withthe clamping means. Preferably the unit comprises two tube straighteningmeans pivotally connected such that in the operating position the drivedirections of both tube straightening means are aligned with each other.

According to a second aspect of the present invention there is provideda method of joining coiled tubing comprising the steps of:

uncoiling a first portion of coiled tubing,

uncoiling a second portion of coiled tubing,

moving the first and second portions into an at least partially enclosedspace,

holding the first and second portions in a clamping means in a positionsuch that the end of the first portion abuts or is close to the end ofthe second portion,

forming a welded connection between said first and second portionswithin said space,

removing the connected first and second portions from said space.

The method may include the step of straightening the coiled tubingbefore clamping it. Preferably the straightening step is achieved bybending the coiled tubing with a reverse curvature opposite to thatwhich it had when coiled. Preferably the amount of reverse curvature isselected such that after bending with the reverse curvature the tubingrelaxes elastically to adopt a substantially straight shape. Preferablythe tubing retains a reverse plastic deformation after the straighteningstep.

Preferably the method includes the step of substantially enclosing theat least partially enclosed space before welding. Preferably the spacecomprises the interior of a container.

Preferably the container comprises one or more slots to permit thepassage of the connected sections of coiled tubing from the container ina direction substantially perpendicular to the longitudinal axis of thecoiled tubing at the connection.

The method may further comprise one or more of the following steps:

driving the first and second portions of tubing towards each other whenclamped until the end of the first portion abuts or is close to the endof the second portion,

applying heat removal clamps to the first and second portions of tubingbefore welding,

inspecting the weld using weld inspection apparatus, such as X-ray,ultrasonic or eddy current equipment.

Thus the invention provides in one embodiment a fabricated containerwhich is well lit and air conditioned, so as to provide both adequateventilation for the welder or operator and a controlled environment forthe welding operation. The coiled tubing and the welder/operator arehoused within a dry, draught free environment, which is a prerequisitefor a high quality weld.

The invention provides the environmental conditions and physicalrequirements to perform an automated weld to join tubing strings in ahostile external environment. The automated weld can be performed usingan orbital welding head which will produce a weld of superior quality,reliability and repeatability in comparison to a manual butt weld.

An embodiment of the invention will now be described, by way of exampleonly, with reference to the accompanying figures, where:

FIG. 1 is a schematic view of a prior art coiled tubing unit;

FIG. 2 is a view of a welded joint between two sections of coiledtubing;

FIG. 3 is a schematic view of an apparatus according to the invention;

FIG. 4 is an isometric view of an apparatus according to a firstembodiment of the invention;

FIGS. 5(a) and 5(b) show the apparatus of FIG. 4 in relation to tworeels of coiled tubing;

FIG. 6 shows the apparatus of FIG. 4 before slide out of the clampingrig and straightening stack;

FIG. 7 shows the apparatus of FIG. 4 after slide out of the clamping rigand straightening stack;

FIG. 8 shows the apparatus of FIG. 4 after rotation of the straighteningstacks to bring them into mutual alignment;

FIG. 9 shows the apparatus of FIG. 4 after rotation of the straighteningstacks with the jaws of one stack open to receive a length of coiledtubing;

FIG. 10 is an enlarged view of the clamping rig and straightening stackof FIG. 9;

FIG. 11 is a view of the clamping rig and straightening stack of FIG. 9after feeding through coiled tubing from both sides;

FIG. 12 is a side view of the apparatus of FIG. 4 after clamping of thetubing and slide in of the clamping rig;

FIG. 13 is a front view of the apparatus of FIG. 4 after heat clampingof the tubing and slide in of the clamping rig;

FIGS. 14 and 15 show the profile of the drive belt and pulley withoutand with the tubing respectively. The spacing of the belts on each jawcan be varied to accommodate different sizes of pipes between the belts;

FIG. 16 is an enlarged view of the clamping rig bogey showing itsrelationship with the runners and moment beam of the platform base;

FIGS. 17(a) to 17(d) show schematically the method of straightening of asection of coiled tubing according to the invention;

FIGS. 18(a) and (b) show a front elevation and side elevationrespectively of an apparatus according to a second embodiment of theinvention;

FIGS. 19(a) to (c) show a front elevation, side elevation and planrespectively of the clamping apparatus of the apparatus of FIG. 18;

FIG. 20(a) shows the clamping apparatus of FIG. 19 in a first position,with the clamped ends of the coiled tubing spaced apart; and

FIG. 20(b) shows the clamping apparatus of FIG. 19 in a second position,with the clamped ends of the coiled tubing brought together in a weldingposition.

Referring to FIG. 3 there is shown an apparatus 10 for use in weldingtogether sections of coiled tubing 6. The coiled tubing 6 is coiled onreels 20, 21, with the apparatus 10 being placed between the two reels20, 21. The apparatus comprises a skid or base 11 on which is mounted ahydraulic scissor lift 12 supporting a platform base 13. Mounted on theplatform base 13 is a platform shell or container 14 which contains aclamping rig and straightening stack. The rig is provided with liftingpoints 15 and stabilising arms 16 which may be extended to increase thestability of the rig when the scissor lift 12 is extended. The rig mayinclude its own power supply 17 and a ladder 18 may be provided foraccess to the container 14 in the raised position.

Referring to FIGS. 4 to 17 there are shown details of an apparatusaccording to a first embodiment of the invention. The skid 11 hasdimensions of approximately 3.0 m×2.4 m×0.3 m (10′×8′×1′). The skid maybe constructed from rolled steel beams and steel sheet. The skid hastelescopic stabilising legs 16 to provide additional operatingstability. The skid supports the bearing housings for the scissor liftbearings, the electrical generator/drive motor 17, battery pack,hydraulic unit, cable/pipe drums, a telescopic ladder 18 to the platformand all other necessary electrical and hydraulic equipment required forthe rig to operate. The electrical cable and hydraulic piping is fed tothe platform base 13 from the skid 11 via drums to allow for thevertical movement of the platform base in relation to the skid 11. Theskid, in short, supports any equipment which does not have to be on therig platform 13 itself.

The scissor lift 12 is an off the shelf item and is mounted on the skid11. The scissor lift 12 is selected to provide the appropriate traveland load capacity, such that the platform shell 14 and all the equipmentcontained therein can be lifted to the appropriate level at whichwelding operations are to be carried out.

The approximate dimensions of the platform base 13 are 2.4 m×2.4 m(8′×8′). Like the skid it may be constructed from rolled steel beams andsteel sheet. The platform base houses the runners 30 for the clampingrig and straightening stack bogeys 35, 36. The bogeys are provided withsupport means such as wheels 70 which are guided along the runners 30,as seen in FIG. 16. The bogeys are of sufficient length so that aportion of the bogey may project beyond the end of the runners while therest of the bogey is still guided by the runners. The clamping rig 31and straightening stack 32, which are positioned at the projecting endof the bogey, are thus able to roll out beyond the edge of the platformbase.

The platform base 13 also supports the beam housing 72 for the bogeymoment beam 71. The beam housing 72 is a rectangular slot situated abovethe runner housing 30 to which the induced bending moment from thecantilevered operation of the clamping rig and straightening stack istransferred by means of a moment beam 71 connected to the bogey 36. Therunner 30 and beam housing 72 form a load bearing member of the platformbase 13.

The hydraulic line and power cable are fed from the skid 11 into therear of the platform base 13 where they feed onto a further pair ofdrums (not illustrated). These drums then feed the hydraulic line andpower cable to the clamping rig 31 and straightening stack 32 in thearea below the runner and beam housing, feeding to one side andreturning from the other. The platform shell 14 is bolted directly ontothe platform base 13.

The platform shell or container 14 is approximately 2.4 m×2.4 m×2.4 m(8′×8′×8′) in size and is formed from sheet steel on three sides 40, 41,42, the fourth side 43 being a shutter which lifts to allow the clampingrig 31 and straightening stack 32 to roll beyond the platform base 13.The shell has a door 44 on each side of the base to allow two means ofentrance and exit from the platform and has a narrow slot 45 (seen inFIG. 12) cut on each side 40, 42 of the shell to allow the coiled tubingto pass through the unit for the purposes of the welding operation. Theshell may be lit internally by fluorescent lighting and may also containdark room lights for film processing. The shell houses the weldinspection equipment, the control panel for the clamping rig andstraightening stack (controlling the movement of the clamping rig andstraightening stack, the operation of the clamping rig and straighteningstack and the control of the cooling air supply to the heat clamps) andprovides a dry, well lit, temperature controlled environment for thewelder. The air inside the platform shell may be circulated and filteredto provide clean air for the welder.

The weld inspection equipment (e.g. X-ray, ultrasonic, eddy current)contained within the unit allows the weld inspector to inspect the weldin situ, immediately after completion of the welding. If required, e.g.for X-ray inspection with the presence of a radioactive isotope, safetyfor this procedure is achieved by the use of inter-locks on the doors,by visible and audible warnings, and by containing the weld and X-rayhead within a lead or tungsten collimator. After the X-ray has beentaken the film may then be processed within the unit using a compactauto-processor, the unit doubling as a dark room. The unit may include alight box for viewing the processed film.

The shell can also house heat treatment equipment for heat treatingwelds after the welding process, as well as other ancillary inspectionequipment.

The clamping rig 31 and straightening stack 32 are powered by hydraulicmotors which drive belts which grip the tubing. The clamping rig andstraightening stack move out beyond the edge of the platform base aspreviously described, where the arms of the straightening stack fold outand the unit performs the straightening operations.

The following sequence of actions describes how the unit typicallyoperates:

1 The rig 10 is positioned between the two reels 20, 21 of coiled tubingto be joined as shown in FIG. 5(a).

2 The rig rises on hydraulic scissor legs 12 to the level of the coiledtubing 6 as it spools off the top of the drum 20, 21 as shown in FIG.5(b).

3 The shutter on the operating side 43 of the rig is opened. FIG. 6shows the shutter in the open position so that the operating side 43between the shutter guide tracks 46 is open.

4 The tubing straightening stack 32 and clamping rig 31 roll out beyondthe edge of the rig platform, on bogeys 35, 36 mounted on runners 30, asshown in FIG. 7. The bogeys 35, 36 are separate, so that the bogey 35supporting the clamping rig 31 may be slid back onto the platform base13 while the bogey 36 supporting the straightening stack 32 remainscantilevered beyond the edge of the platform base 13. The independentoperation of the bogeys 35, 36 may be achieved by mounting one bogey 35on top of the other bogey 36, or by mounting the clamping rig bogey 35on separate runners 30 positioned inside the runners 30 used by thestraightening stack bogey 36.

5 The tubing straightening stack 32 comprises two straightening arms 37,37′ which rotate about a vertical pivot axis, so that the stack foldsopen and each arm 37, 37′ is aligned with the tubing 6 as it is pulledoff the drum as shown in FIG. 8. It is possible that the straighteningstack 32 may comprise only one arm 37, if it is not necessary tostraighten coiled tubing 6 on both sides of the connection.

6 The end of the tubing 6 on the first reel 20 is now attached to a wire26 by means of a clamp 28. The wire 26 passes over a pulley 27 to apowered winch 25 which is incorporated in the clamping rig 31. The winchis operated to drag in the coiled tubing 6 between the jaws 38, 38′ ofone of the arms 37 of the straightening stack 32, as shown in FIG. 9.

7 The jaws 38, 38′ of the straightening stack 32 hinge open to allow thetubing to be more conveniently fed into the stack, as shown in FIG. 10.

8 The jaws 38, 38′ (shown schematically in FIG. 11) are closed aroundthe tubing 6 which is then driven through the straightening stack 32 andthe clamping rig 31, emerging in the clamping area 50. Each jaw 38, 38′comprises a drive belt 39, 39′ which is arranged to have an arcuateform, with a curvature which is opposite to that of the tubing. Hence asthe tubing 6 is driven through the jaws it is deformed elastically thenplastically such that the curvature is reversed. When the tubing emergesfrom the jaws there is an elastic relaxation, resulting in the tubing inthe clamping area 50 being linear, as shown in FIG. 11.

FIGS. 17(a) to (d) show how the coiled tubing is deformed by thestraightening stack. FIG. 17(a) shows the tubing in its coiled form onthe reel. The upper side 61 has been plastically deformed during thereeling operation so that even after unreeling it is longer than thelower side 62 of the coil. If the tubing is straightened elastically asin FIG. 17(b), the fact that the upper side 61 is longer means that theend 63 of the tubing is not square and welding a connection isdifficult. According to the invention the reverse bending effected bythe straightening stack results in permanent plastic elongation of thelower side 62 of the tubing (see FIG. 17(c)), so that, after passingthrough the jaws to the clamping area, on elastic relaxation the upperand lower sides 61, 62 are of equal length and the end 63 of the tubingis square.

9 Steps 6 through 8 are then carried out for the second tubing reel 21on the other side of the rig.

10 The jaws 38, 38′ on both arms 37, 37′ of the straightening stack 32then open again releasing the tubing 6 which is now held by clamps 29 inthe clamping rig 31.

11 The clamping rig 31 and the straightening stack 32 now separate. Theclamping rig, with clamps 29 gripping the tubing 6, moves inside the rigplatform on the clamping rig bogey 36, while the straightening stack 32remains external. The shutter of the container 14 closes after theclamping rig has moved inside, as shown in FIG. 12. The slot 45 in theside of the container 14 allows passage of the tubing 6 whose end isclamped in the clamping rig 31, when the clamping rig moves inside thecontainer 14. The ends 63 of the tubing are prepared for welding, e.g.by grinding.

12 The tubing 6 is now driven by the clamping rig 31, whose clamps 29accommodate driving movement, until the two ends 63 are close enough toweld.

13 The heat sink clamps 51, which are designed to remove heat from thewelded area of the tubing 6, are closed around the protruding ends ofthe tubing, as shown in FIG. 13.

14 The tubing is welded together.

15 The weld inspection using X-ray equipment is carried out inside therig platform. The processing of the film and viewing of the processedfilm are also carried out in the container 14.

16 The weld is inspected, the shutter is opened, the clamping rig 31moved outside the rig platform 14 and, if the weld is found to besatisfactory, the tubing 6 is released from the clamping rig 31.

17 in the situation where the weld is not satisfactory the tubing 6 iscut and the procedure recommences from step 12.

The procedure of steps 6 to 8 can be automated. The operator selects thediameter, thickness and material properties of the coiled tubing to bestraightened. The clamping force and driving force applied by the belts39, 39′ on jaws 38, 38′ is then calculated automatically, and sensorsensure that the correct clamping force is maintained and that the tubingis pulled through the straightening jaws at the correct rate. Althoughthe FIGS. 9 and 10 show the jaws of the straightening arm being hinged,they may be separated by other means, such that they move in parallelrelation to one another. In particular their separation may be variableto accommodate different size pipes. FIGS. 14 and 15 show opposing belts39 and 39′ in end view. The drive surface of each belt has a concaveshape 55 in the transverse direction, such that the belt can accommodatetubing 6 of different diameter. The smaller the diameter of the tubing6, the smaller will be the spacing d between opposing belts 39, 39′.

Referring to FIGS. 18 to 20, there is shown an apparatus according to asecond embodiment of the invention. The apparatus functions in a similarway to that shown in FIG. 3, with the skid base 11 being placed inposition and stabilised by stabilising legs (not shown). Like componentshave the same reference sign. The container 14 is raised on the scissorlegs 13 to the desired level between the reels 20, 21. In the secondembodiment the enclosed container 14 has a vertical tubing slot 45 a ineach side wall and a corresponding slot 45 b in the roof.

The end sections 80, 81 of the coiled tubing from the reels 20, 21 aredrawn in under tension by the winch motor 70 and drum 71, through theside slots 45 a. The winch cable 27 is attached to the ends 82, 83 ofthe CT by way of a modified connector (not shown). The end sections 80,81 of the tubing are located and fixed in the clamps 67 of the clampingunit 72.

The clamping unit 72 is fixed within the container 14 and comprises twosupport legs 60 mounted on the platform base 13. A clamp base 62 ispivotally mounted by hinges 61 to the support legs 60. At one end of theclamp base 62 there is fixed a static clamp assembly 65, having twohydraulically operated clamps 67. At the other end of the clamp base 62there is fixed a drive ram 63 which operates a moving clamp assembly 64,having a further two hydraulically operated clamps 67. The moving clampassembly 64 is restrained to move along one axis by guides 66 whichengage with the static clamp assembly 65.

The static clamp assembly is adjustable, allowing movement of theclamped CT section 81 in two directions perpendicular to the tubing axisand permitting accurate alignment of the tubing ends. The hinge 61allows the joining of tubing which passes through the unit at an angleto the horizontal. Tubing of different sizes can be clamped usingvarious shoe inserts (not shown) which fit into the clamps 67. The shoeshave a semicircular cross section and so can be split to release thejoined tubing string on completion of the weld.

In operation the connectors (not shown) are removed from the ends 82, 83of the coiled tubing, and the ends 82, 83 are prepared for welding,either manually or by an automatic weld preparation tool (not shown).The moving clamp assembly 64 can then be moved in the longitudinaldirection of the tubing so the ends 82, 83 are “mated up” for thejoining operation.

The welding operation is carried out by butt welding manually or bycreating an automated orbital weld. The automated orbital weld is themost desirable method of joining tubing and will therefore be the methodused in most situations.

The inspection and automated diagnosis is then carried out within thecontainer, using any suitable manual or automated method of inspection,such as by X-ray, ultrasound or eddy current measurement. The inspectionequipment may also be used for the continuous inspection of the tubingstring as opposed to simply inspecting just the butt weld.

If the weld fails the QA inspection, the welded portion of tubing can becut out of the string while the CT is still held by clamps 67, so thatthe appearance is as in FIG. 20(a). After preparation of the ends, themoving clamp assembly 64 then brings the two recut ends into the weldposition of FIG. 20(b) and the welding operation can be performed again;this can be done with minimal time delay.

After satisfactory completion of the weld, the unit is lowered on thescissor legs, the joined CT string emerging from the slot 45 b in theroof of the unit. The slots 45 a and 45 b are preferably provided withresilient sealing means such as opposing stiff rubber or synthetic flapsor diaphragms which project from each side, so that the slot resealsaround the tubing as the tubing passes through the slot.

The method afforded by the present invention offers significantadvantages over the prior art methods. In particular, the fact thatwelding and weld inspection can be carried out in a sealed environmentenables the achievement of superior weld quality. It makes possible theuse of enhanced inspection techniques, which would not be practicableusing prior art methods of joining coiled tubing.

There is no need for scaffolding and therefore the associatedexpenditure and cost in lost time are negated.

After the welder has completed his task and because the weld iscontained in a sealed environment, the container can be used to carryout the Q.A. Inspection immediately, with no delay.

A further advantage arises in the fact that the butt weld between thetwo strings of CT can be performed under conditions of relatively hightension in comparison to the current tensile loading of the tubing; thishas a straightening effect on the tubing, resulting in improved physicalproperties of the weld and the tubing adjacent to the weld.

Within the container there may be housed X-Ray inspection equipment anda facility to process the radiographs of the weld automatically, and toview the results.

The prior art system employs Gamma Radiography using a portable Iridium192 Isotope which is expensive, time consuming and of an inferiorquality to the X-Ray Radiography, which may be used in the presentinvention. Gamma Radiography requires barriers to be placed in orderthat access to the pipe deck and rig floor is prohibited, because of therisks of radiation. Other operations on the deck have to cease while theweld inspection takes place. In contrast the method of the invention ismuch safer. The whole process takes place in an enclosed unit, and otheractivities can continue simultaneously on the pipe deck and rig floor.

In the offshore environment, the joining of two sections of coiledtubing according to the method of the invention can be finished withinthree hours, from start to finish. This compares with a typical time of15 hours taken by prior art methods, which have to include the followingsteps:

1 Build Scaffold

2 Set up coiled tubing for welding

3 Weld joint

4 Set up for Radiography, eg permits, barriers, warnings prior to start

5 Carry out radiography and remove equipment from area eg IR192 Isotope

6 Manual developing of film and interpretation of film

7 Stripdown of scaffolding, provided weld has passed stringent Q.A.procedures

The invention enables users of coiled tubing to have confidence inwelded joints in coiled tubing, since the reliability of welds in coiledtubing is enhanced. Presently there is little confidence in weldedjoints in coiled tubing, and they are prone to failure.

The method of the present invention can accommodate other inspectionmethods. As improved inspection methods are developed, equipmentrequired for these methods may be installed in the unit according to theinvention. The method may include continuous inspection of the coiledtubing, for example by electromagnetic inspection techniques.

It should be noted that any features of the embodiment of FIGS. 18 to 20may be combined with any features of the embodiment of FIGS. 4 to 16.

These and other modifications and improvements can be incorporatedwithout departing from the scope of the invention.

What is claimed is:
 1. A portable unit for on-site welding of sectionsof coiled tubing comprising a container for carrying out weldingoperations therein, a tube clamping rig located inside said containerand adapted to clamp two sections of tubing in abutting end to endrelationship, and welding apparatus; said container having a roof, twoopposing side walls and at least one door therein; wherein said tubeclamping rig is adapted to hold and move a first one of said sections oftubing axially into abutting end to end relationship with a second oneof said sections of tubing, and wherein said tube clamping rigcomprises: a first moveable clamp assembly adapted to hold and move saidfirst one of said sections of tubing axially into abutting end to endrelationship with said second one of said sections of tubing; and asecond clamp assembly adapted to hold said second section of tubing. 2.A unit according to claim 1, wherein each of said opposing side wallshas a slot therein, each of said slots being adapted to allow thepassage of a tube extending through said wall and clamped by said tubeclamping rig, such that said tube may move relative to said container.3. A unit according to claim 2, wherein said slots are substantiallyhorizontal and extend to an opening in an end wall of said container. 4.A unit according to claim 2, wherein said slots are substantiallyvertical and extend to a further slot provided in said roof.
 5. A unitaccording to claim 1, further comprising means for adjusting the heightof said container.
 6. A unit according to claim 1, further comprising aclamping rig guide means adapted to guide the tube clamping rig betweena first position outside the container and a second position inside thecontainer.
 7. A unit according to claim 1, further comprising a winchadapted to pull the tubing towards the tube clamping means.
 8. A unitaccording to claim 1, further comprising a tube straightening means. 9.A unit according to claim 1, further comprising a weld inspection means.10. A unit according to claim 1, wherein said welding apparatus is anautomatic welding apparatus.